1. Field of the Invention
The present invention relates to an alternator driven by an internal combustion engine, for example, and in particular, relates to a stator construction for an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck.
2. Description of the Related Art
FIG. 19 is a partial front elevation of a conventional stator mounted in an automotive alternator viewed from an inner circumferential side, and FIG. 20 is a perspective of part of the conventional stator mounted in an automotive alternator viewed from a front side.
In FIGS. 19 and 20, a stator 50 includes: a cylindrical stator core 51 formed with a number of slots 51a extending axially at a predetermined pitch in a circumferential direction; a stator winding 52 wound onto the stator core 51; and insulators 53 installed in each of the slots 51a for electrically insulating the stator winding 52 from the stator core 51. Although not shown, in this conventional example a rotor has 12 poles, and the stator 50 has thirty-six slots 51a, which is one slot per pole per phase.
The stator winding 52 is constructed by connecting in series a number of coil segments 55 composed of short lengths of insulated electrical conductor. Each of the coil segments 55 is formed in a general U shape consisting of a pair of leg portions 55a joined by a turn portion 55b.
The coil segments 55 are inserted two at time from a rear end of the stator core into sets of slots 51a three slots apart. At that time, four leg portions 55a are housed in each slot 51a so as to line up in a row in a radial direction. Each of the coil segments 55 on the inner circumferential side is inserted into a first position from the inner circumferential side of a first slot 51a and a second position from the inner circumferential side of a second slot 51a three slots away, and each of the coil segments 55 on the outer circumferential side is inserted into a third position from the inner circumferential side of the first slot 51a and a fourth position from the inner circumferential side of the second slot 51a three slots away. In other words, the coil segments 55 are housed in sets of slots 51a three slots apart so as to be in different layers.
Next, each of the coil segments 55 is bent such that free ends 55c extending outwards from a front end open outwards in a circumferential direction. Then, free ends 55c of coil segments 55 extending outwards from the front end from the first position from the inner circumferential side of the slots 51a are stacked in a radial direction with the free ends 55c of coil segments 55 extending outwards from the front end from the second position from the inner circumferential side of slots 51a three slots away, and are joined by soldering or laser welding. Two inner circumferential coils consisting of six coil segments 55 connected in series are thus obtained.
Similarly, free ends 55c of coil segments 55 extending outwards from the front end from the third position from the inner circumferential side of the slots 51a are stacked in the radial direction with the free ends 55c of coil segments 55 extending outwards from the front end from the fourth position from the inner circumferential side of slots 51a three slots away, and are joined by soldering or laser welding. Two outer circumferential coils consisting of six coil segments 55 connected in series are thus obtained.
These inner and outer circumferential coils are connected in series to form one phase of coil having 4 turns.
Furthermore, two other phases of coil are also formed in a similar manner.
The stator winding 52 is formed by connecting these three phases of coil into an alternating-current connection.
As shown in FIGS. 19 and 20, in the stator 50 constructed in this manner, the coil ends formed by joining the free ends 55c of the coil segments 55 to each other are mutually spaced and arranged in neat rows in a circumferential direction and constitute front-end coil end groups 52a. The coil ends consisting of the turn portions 55b of the coil segments 55 are mutually spaced and arranged in neat rows in a circumferential direction and constitute rear-end coil end groups 52b.
In the conventional stator 50, because the front- and rear-end coil end groups 52a and 52b are constructed by mutually spacing and circumferentially arranging coil ends which connect outside the slots different layers in slots 51a three slots apart, axial heights of the front- and rear-end coil end groups 52a and 52b have been raised and irregularities in the circumferential direction have arisen on the inner circumferential side of the front- and rear-end coil end groups 52a and 52b.
Thus, when this stator 50 is mounted in an alternator, the disadvantages described below arise, and a problem has been that improvements in reliability, increases in performance, and reductions in cost have not been possible.
Namely, there is a risk that foreign matter will infiltrate the coil end groups 52a and 52b through gaps between the coil ends, damaging the insulation on the electrical conductors and degrading insulation quality.
Furthermore, the longer the axial length of the coil end groups 52a and 52b, the greater the wind resistance against the cooling air flowing around the coil end groups 52a and 52b, reducing cooling quality, allowing the temperature of the stator winding 52 to increase excessively.
Also, the longer the axial length of the coil end groups 52a and 52b, the greater the coil resistance and coil end leakage reactance, reducing output, increasing copper loss, and also reducing efficiency.
Because there are circumferential irregularities on the inner circumferential side of the coil end groups 52a and 52b, interference noise between the coil end groups 52a and 52b and the rotor is increased, increasing wind noise.
In addition, the amount of copper constituting the material of the stator winding 52 is increased, causing cost increases.
Moreover, the greater the number of sots per pole per phase, the greater the axial length of the coil end groups, exacerbating the above disadvantages.